This project is designed to investigate the spatial distribution and functional properties of cortical neuron "colonies" in the primate motor cortex and supplementary motor area that project to the spinal cord and are associated with individual muscles or closely related groups of muscles, as well as the activity of neurons in such colonies during defined voluntary motor behaviors. Cortical cell discharge patterns during normal movements are evaluated in terms of EMG patterns, and their responses to small loading and unloading torque perturbations. Spinal cord location of motoneurons innervating selected forelimb muscles and termination patterns in the spinal cord and brainstem of sensory receptors within these muscles are studied using anterograde and retrograde tracing methods.